256 COLORATION [CH. 



markings in black, dark brown, or deep olive-green (e.g. many 

 Agrionidae and Lestidae). The most beautiful larvae of all are 

 those of Anax 1 , dwelling freely in water-weed, with their dark 

 olive-green patterns on a rich green ground-colour. Larvae that 

 dwell on sticks may become dark brown or even jet-black, with 

 either partial or entire secondary loss of their pattern (e.g. many 

 Brachytronini). Rock-dwellers are either black, dark grey or 

 brown, according to the colour of the rocks which they frequent. 



It is a fact that Dragonfly larvae can change their colours to 

 suit their environment. To shew this, it is only necessary to 

 take larvae of the same species of Libellulidae from, say, a pool 

 in a chalk-pit and a neighbouring pond with dark bottom-soil. 

 The latter will be found to be twice as dark as the former. An even 

 more startling colour-change came to my notice one year in the 

 case of Aeschna brevistyla. This larva is of an almost uniform 

 brown tint. It happened that a small dam was newly formed. 

 Masses of the reeds, dug out from the banks, floated on the surface 

 of the water. As these decayed, their root-stocks and roots became a 

 bright brick-red. On hauling them ashore I found six Aeschna larvae 

 clinging to them. All of these had their ventral surfaces, including 

 the mask and the undersides of the legs, a rich brick-red. Other 

 larvae from the sides of the dam were of the normal brown colour. 



These larvae, placed in my aquaria, remained red until the 

 next ecdysis, when they resumed their brown colouring. Hence 

 it is clear that the change is not produced voluntarily, through 

 the eye, as in the case of the Chameleon, but is due solely to what 

 I may term a chemical plasticity on the part of the fresh pigments 

 formed at ecdysis. When freshly formed, it seems clear that this 

 pigment can be turned red by red surroundings (as in the case of 

 the red light from the dead reeds acting on the pigment of the 

 Aeschna larva), brown by brown surroundings, black by black, or 

 green by green. Whether the change would extend to blue, orange 

 or purple, we do not know. I think that a similar plasticity, at 

 metamorphosis, has helped to determine the formation of hylo- 

 chromes and heliochromes in the imagines. 



1 It is a peculiar fact that these larvae, when young, dwell on twigs or matted 

 roots, and are often found to be whitish, marked with black in broad transverse 

 bands. Later on, they migrate to floating weed-masses and become mottled green. 



